Haunting Miss Trentwood

Mary Trentwood is horrified when she watches her father crawl from his grave the day of his funeral. Mistaking the newly-arrived Alexander Hartwell to be her father's solicitor, Mary welcomes him into her home, not realizing he hunts a blackmailer. Why is Trentwood's ghost determined to make everyone think Mary is insane? Why is Hartwell snooping around Mary's home rather than looking over Trentwood's papers? Who is the blackmailer, and what are they doing in Mary's home?